A Universal Mobile Telecommunication System (UMTS) is a broadband, packet based system for the transmission of text, digitized voice, video and multi-media. It is a highly subscribed to standard for third generation and is generally based on Wideband Coded Division Multiple Access (W-CDMA).
In a UMTS network, a Radio Resource Control (RRC) part of the protocol stack is responsible for the assignment, configuration and release of radio resources between the UE and the UTRAN. This RRC protocol is described in detail in the 3GPP TS 25.331 specifications. Two basic modes that the UE can be in are defined as “idle mode” and “UTRA RRC connected mode” (or simply “connected mode”, as used herein). UTRA stands for UMTS Terrestrial Radio Access. In idle mode, the UE or other mobile device is required to request a RRC connection whenever it wants to send any user data or in response to a page whenever the UTRAN or the Serving General Packet Radio Service (GPRS) Support Node (SGSN) pages it to receive data from an external data network such as a push server. Idle and Connected mode behaviors are described in detail in the Third Generation Partnership Project (3GPP) specifications TS 25.304 and TS 25.331.
When in a UTRA RRC connected mode, the device can be in one of four states. These are:
CELL_DCH: A dedicated channel is allocated to the UE in uplink and downlink in this state to exchange data. The UE must perform actions as outlined in 3GPP 25.331.
CELL_FACH: no dedicated channel is allocated to the user equipment in this state. Instead, common channels are used to exchange a small amount of bursty data. The UE must perform actions as outlined in 3GPP 25.331 which includes the cell selection process as defined in 3GPP TS 25.304.CELL_PCH: the UE uses Discontinuous Reception (DRX) to monitor broadcast messages and pages via a Paging Indicator Channel (PICH). No uplink activity is possible. The UE must perform actions as outlined in 3GPP 25.331 which includes the cell selection process as defined in 3GPP TS 25.304. The UE must perform the CELL UPDATE procedure after cell reselection.URA_PCH: the UE uses Discontinuous Reception (DRX) to monitor broadcast messages and pages via a Paging Indicator Channel (PICH). No uplink activity is possible. The UE must perform actions as outlined in 3GPP 25.331 including the cell selection process as defined in 3GPP TS 25.304. This state is similar to CELL_PCH, except that URA UPDATE procedure is only triggered via UTRAN Registration Area (URA) reselection.
The transition from an idle mode to the connected mode and vice-versa is controlled by the UTRAN. When an idle mode UE requests an RRC connection, the network decides whether to move the UE to the CELL_DCH or CELL_FACH state. When the UE is in an RRC connected mode, again it is the network that decides when to release the RRC connection. The network may also move the UE from one RRC state to another prior to releasing the connection or in some cases instead of releasing the connection. The state transitions are typically triggered by data activity or inactivity between the UE and the network. Since the network may not know when the UE has completed the data exchange for a given application, it typically keeps the RRC connection for some time in anticipation of more data to/from the UE. This is typically done to reduce the latency of call set-up and subsequent radio resource setup. The RRC connection release message can only be sent by the UTRAN. This message releases the signal link connection and all radio resources between the UE and the UTRAN. Generally, the term “radio bearer” refers to radio resources assigned between the UE and the UTRAN. And, the term “radio access bearer” generally refers to radio resources assigned between the UE and, e.g., an SGSN (Serving GPRS Service Node). The present disclosure shall, at times, refer to the term radio resource, and such term shall refer, as appropriate, to either or both the radio bearer and/or the radio access bearer.
The problem with the above is that even if an application on the UE has completed its data transaction and is not expecting any further data exchange, it still waits for the network to move it to the correct state. The network may not be even aware of the fact that the application on the UE has completed its data exchange. For example, an application on the UE may use its own acknowledgement-based protocol to exchange data with its application server, which is accessed through the UMTS core network. Examples are applications that run over User Datagram Protocol/Internet Protocol (UDP/IP) implementing their own guaranteed delivery. In such a case, the UE knows whether the application server has sent or received all the data packets or not and is in a better position to determine if any further data exchange is to take place and hence decide when to terminate the RRC connection associated with Packet Service (PS) domain. Since the UTRAN controls when the RRC connected state is changed to a different state or into an idle mode and the UTRAN is not aware of the status of data delivery between the UE and external server, the UE may be forced to stay in a higher data rate state or mode than what is required, possibly resulting in decreased battery life for the mobile station and also possibly resulting in wasted network resources due to the fact that the radio resources are unnecessarily being kept occupied and are thus not available for another user.
One solution to the above is to have the UE send a signaling release indication to the UTRAN when the UE realizes that it is finished with a data transaction. Pursuant to section 8.1.14.3 of the 3GPP TS 25.331 specification, the UTRAN may release the signaling connection upon receipt of the signaling release indication from the UE, causing the UE to transition to an idle mode or some other RRC state. A problem with the above solution is that the UTRAN might become inundated with signaling release indication messages from the UE and other UEs